Ferritic-pearlitic Steel Research Articles

The Structure of Grain Boundaries and the Processes of Failure in the Ferrite-Pearlitic Steels

Influence of a structure with intergranular grain boundaries on mechanical properties and development of impact and fatigue failure processes were considered on an example of St3 steel. Fractographic studies showed that a brittle component is observed during impact fracture when the presence of knife-like boundaries inside the ferrite grains take place, the rate of growth of fatigue cracks increases.

構造用鋼 ベイナイト型非調質鋼の組織と機械的性質に及ぼす合金元素の影響と切欠き材の疲労強度

Influence of carbon, manganese, chromium, and vanadium contents on mechanical properties and microstructures of bainitic microalloyed steels are investigated. The fatigue limit of the bainitic steels were compared with the ferritic-pearlitic steels with smooth and notched specimens. The hardness are increased by increase in content of each alloying element. The carbon equivalent for hardness (Ceq) can be described by the following equation Ceq=C(mass%)+0.23 ×Mn(mass%)+0.26 ×Cr(mass%)+0.31 × V(mass%). Carbon, manganese, and chromium decrease toughness but vanadium improves both toughness and hardness. Additionally, vanadium is effective in improvement of 0.2% proof. This reason is estimated that microstructures of bainitic steel i.e. martensite-austenite constituent (M-A constituent) are refined by vanadium addition. The fatigue strength of bainitic steels with smooth specimen is lower than ferritic-pearlitic steels for the same hardness. However, it is higher in the case of notched specimen. This is because bainitic steels have better notch sensitivity.

The influence of martensite on the strength and impact behavior of steel

The influence of high C martensite on the strength and impact behavior of C-Mn-Nb-Al steels has been determined for two distributions: films surrounding the ferrite grains and distinct colonies. In the former case, the impact behavior markedly deteriorated, this deterioration increasing with martensite level. The changes in impact behavior could be explained by regarding the films of martensite as being similar to the brittle grain boundary carbides that are present in ferrite-pearlite steels. These films readily crack, yet are always thick enough to produce a sufficiently wide crack to render crack propagation easy. The critical event in fracture then becomes the ability to propagate the cracks through the grain boundaries. The greater the grain boundary coverage by these films, the easier this becomes and the worse is the impact behavior. When the martensite is present as colonies, again the impact performance is seriously impaired, but to a lesser extent than when the martensite is present as films, this probably being related to the difficulty in cracking a thick colony except at its extremities. The influence of martensite on strength was found to be similar whether the martensite was in the form of colonies or films. Replacing pearlite with martensite led to a large increase in the yield strength. Increasing the amount of martensite to ∼7 pct caused the yield strength to fall to a minimum, after which it again increased. This behavior can be interpreted in terms of the manner in which the volume expansion accompanying the martensite transformation influences the generation of dislocations.

Subsurface characteristics of an abraded low carbon steel

Ductile metals commonly exhibit plastic deformation at and near the worn surface and their flow behaviour at large strains has a clear effect on wear resistance. In this study, the characteristics of the near-surface region of a ferritic-pearlitic steel (0.2% C, 1.2% Mn), subjected to abrasive wear tests, were examined. Wear tests were performed under different loads by rubbing the specimens on sliding 60 mesh Al 2O 3 abrasive band. The metallographic technique used to determine the magnitude of plastic deformation was based on measurement of the displacements of pearlite bands. The hardness of the plastic deformation zone was determined by performing ultramicrohardness tests along ferrite bands with a Vickers indenter. Microscopic examinations of the near-surface regions revealed the wear mechanism to be ploughing and the deformation mechanism to be cross-slip. It was observed that plastic strain (more than 6) occurred on the abraded surface, and increased the hardness to about 1.5 times the original value. The strain and hardness gradient extended to a larger depth into the bulk with increasing wear test load. It is concluded that the wear resistance of the investigated steel increases by work hardening of the near-surface region which is required to consume high energy for abrasion, during sliding. Ultramicrohardness measurements performed on worn specimens revealed high hardness, as the indent size decreased. The indentation size-hardness relation was explained by a dislocation model incorporating geometrically necessary dislocations due to the presence of strain gradients in the deformation region around the indent.

Influence of grain boundary films of martensite on strength and impact behaviour of ferrite

The influence of thin films of martensite at the ferrite grain boundaries on the impact behaviour and strength of a high manganese–niobium containing steel has been examined. Normalising followed by intercritical annealing, at 730°C for various times from 0 to 900 min, and quenching introduced these martensite films. The percentage of martensite increased with increased holding time at 730°C from 15 to 33 vol.-%. The introduction of martensite removed the yield point but the yield strength was little affected, increasing only slightly with an increase in martensite volume fraction. In contrast, the impact behaviour markedly deteriorated when martensite was present, but when the amount of martensite further increased above 15 vol.-% it only had a small detrimental influence. The changes in impact behaviour could be explained by regarding the thin films of martensite as being similar to the brittle grain boundary carbides present in ferrite–pearlite steels. These martensite films readily crack yet are always thick enough to produce a sufficiently wide crack to render crack propagation easy and the critical event in fracture then becomes the ability to propagate the cracks through the grain boundaries.

On the development of a relation between fractal dimension and impact toughness

Fractal characterization is an increasingly important method in fractography. This paper presents the results of a study made on the relation between the fractal dimensional increment (Df′), as measured by the slit island technique, and the impact toughness in a commercial medium-carbon ferrite-pearlite steel. Charpy V-notch samples with different thermomechanical treatments were tested at room temperature and demonstrated a positive relation between Df′ and the impact energy. This study includes consideration of fracture micromechanism factors for which Df′ cannot always be positively related to the toughness.

Structure of the Bonding Zone in Explosively Welded Austenitic and Ferrite-Pearlitic Steel / Gefüge der Verbundzone in sprengplattiertem austenitischem und ferritisch-perlitischem Stahl

The structure of the bonding zone in explosively welded joints of ferrite-pearlite steel (0,3 % C, 1,4 % Mn) as a target and austenitic nitrogen steel (0,64 % N, 18 % Cr, 12 % Mn) as a flyer was studied by transmission electron microscopy. For the observation of the flyer a model joint was prepared using equal plates of the Cr-Mn-N steel for the flyer and the target. The structure of both joints had a layer character. The bonding was realized by a thin layer containing ultra-fine equiaxial recrystallized grains: ferritic in the real joint and austenitic in the model joint. The flyer structure was built up by parallel layers of plastically deformed austenite. A combined action of plastic deformation and heating was found in the regions of target close to the interface. Depending on the local conditions it caused formation of dislocation cell structure, polygonisation or recrystallisation in the ferrite, partial dissolution of cementite and secondary precipitation of dispersed carbides. The structure of the target suffered only the influence of cold deformation at a distance larger than 0,3 to 0,5 mm from the interface, which caused martensitic transformation in the layer between 0,5 and 1,0 mm from the interface.

Contribution to the comparative analysis of some periodical multiaxial criteria [Contribution a l'analyse comparative de criteres de fatigue multiaxiaux periodiques: Fogue, M., Robert, J.-L. and Bahuaud, J. Mecanique Indust Materiatux (1995) 48, 136–139

The process of ductile crack initiation has been investigated for a ferritic, pearlitic and a bainitic structural steel. A three-dimensional analysis has revealed that the ductile crack initiation occurs by formation of disconnected microcracks along the crack front. While the distribution of inclusions and highly strained regions governs the microcracking in the ferritic-pearlitic steel, the geometrical inhomogeneities produced by fatigue precracking act as the sites for formation of microcracks in the bainitic steel. In the latter steel, the size of the carbides is two orders of magnitude smaller than the crack tip opening produced by fatigue precracking, and hence, ductile crack initiation can not be modeled as the coalescence of the first microvoid with the crack tip.

Fatigue life studies in carbon dual-phase steels

An investigation has been conducted to examine the morphological influence on fatigue life of low carbon steel with dual phase microstructure. The results showed that dual-phase microstructure, composed by ferrite and martensite had superior symmetrical bending fatigue strength when compared with ferrite-pearlite steel. Through those tests, evidences of different mechanisms were verified (such as ferrite cyclic hardening, slip band formation and beginning of crack nucleation and propagation). Based on the fatigue tests results, various mechanisms stages were discussed associated with different microstructure morphology.

Hydrogen embrittlement of ferrite-pearlite steels during drawing

Methods of transmission electron microscopy are used to establish the influence of preliminary surface decontamination on the microstructures of 20G2R and 30G1R steels after drawing and stamping. We explain how surface hydrogenation during decontamination by acid media leads to penetration of hydrogen into the metal and leads to an increase in long-range stress fields and formation of micropores and microcracks. We analyze the effect of the quantitative statistical characteristics of substructure evolution of steels with different contents of carbon and alloying elements. We consider possible mechanisms for hydrogen hardening of steel.

Ductile crack initiation in steels

The process of ductile crack initiation has been investigated for a ferritic, pearlitic and a bainitic structural steel. A three-dimensional analysis has revealed that the ductile crack initiation occurs by formation of disconnected microcracks along the crack front. While the distribution of inclusions and highly strained regions governs the microcracking in the ferritic-pearlitic steel, the geometrical inhomogeneities produced by fatigue precracking act as the sites for formation of microcracks in the bainitic steel. In the latter steel, the size of the carbides is two orders of magnitude smaller than the crack tip opening produced by fatigue precracking, and hence, ductile crack initiation can not be modeled as the coalescence of the first microvoid with the crack tip.

Adsorption of Octadecyldimethylbenzylammonium Chloride to Two Carbon Steel Microstructures as Observed with Surface-Enhanced Raman Spectroscopy

Abstract Adsorption of the inhibitor octadecyldimethylbenzylammonium chloride (ODBAC) to two carbon steel microstructures, one ferritic-pearlitic and one martensitic, in 0.15 M sodium carbonate (Na2CO3) + 0.15 M sodium bicarbonate (NaHCO3) solution of pH 10 was investigated using surface-enhanced Raman spectroscopy (SERS). ODBAC physisorbed strongly to the ferritic-pearlitic steel and weakly to the martensitic steel. A weak metal-ODBAC bond formed between the metal surface and the ODBAC ring substituent, oriented at an inclined angle to the metal surface. Physisorption of ODBAC was found to depend upon potential, and this was correlated to the potential-dependent presence of magnetite (Fe3O4).

Strain hardening of steels at large strain deformation. Part I: Relationship between strain hardening and microstructures of b.c.c. steels

In the present work, the relation between strain hardening behaviour and microstructure of steels, especially for large deformations, was investigated with the help of the Kocks model. First, the different origins of flow stresses and the development of the dislocation density are discussed because of their importance to the Kocks model. For the measurement of stress strain curves at large deformations, a new method of tensile testing was developed. Steels with different but defined microstructures were produced. It was found that the strain hardening behaviour of Ti micro-alloyed steels and ferritic pearlitic steels depends significantly on the microstructure. Small precipitates or increasing volume fraction of hard second phase increase the strain hardening rate. A quantitative characterization of the microstructure of well-annealed steels can be given by the yield stress and the relation between strain hardening and microstructure can be replaced by the relation between strain hardening and yield stress.

The effect of the grain size of the ferritic-pearlitic steel 45 on the parameters of its fracture under impact loading

The article investigates the influence of the grain size of the ferritic-pearlitic steel 45 with standard composition in the range 2–50 Μm on the parameters of the energy of crack nucleation and propagation in the process of impact loading in the temperature range from −100 to +150‡C. It is shown that reduction of the grain size from 50 to 2 Μm has no effect on the fracture energy and on the “true” specific values of impact toughness at temperatures inducing completely brittle or ductile fracture, and that it increases the fracture energy and KCVtru solely in the region of temperatures of the viscobrittle transition. Dissipation of the fracture energy expanded on the nucleation of secondary cracks and microcracks has no significant effect on the KCVtru of the steel in all the examined ranges of grain sizes and temperatures. The article notes the structural insensitivity of the process of crack and microcrack nucleation in steel 45 under dynamic loading.

Microstructure and deformability of steels

Microstructural analysis of the deformability of steels and alloys has been insufficiently well investigated despite the to that a specified plasticity often cannot be achieved without providing the requisite stress state. The article presents data on a structural analysis of the deformability of steels of different classes that has been conducted by the Department of Heat Treatment and Metal Physics in cooperation with the Department of Pressure Treatment of Metals at the Urals State Engineering University. The article is devoted to microstructural aspects of the deformability of structural steels. It is shown that the diagram of the stress state should be taken into account in analyzing the effect of structural factors. The dependence of the mechanism of strengthening of ferrite-pearlite steels on the grain size and the effect of the content of pearlite on their strength properties are established.

Improvement of microstructure in forging of a connecting rod by means of finite element simulations

Precipitation hardening ferritic pearlitic steels are used in forged engine and undercarriage components in the automotive industry. The required properties are attained by controlled cooling from forging heat, saving time and cost consuming heat treatments. Therefore, before phase transformation the desired austenitic condition has to be attained during the preceding forming operations. Designing multi-step forging schedules with a view to avoiding inhomogeneities by conventional trial and error strategies is time consuming, expensive and does not always lead to optimum results. It is therefore desirable to gain information on the evolving microstructure of a process by means of computer simulations. An enhanced process layout can then be found by variation computations. In the present work such a model is introduced and applied to the production of a connecting rod of steel 49MnVS3. The computed results are compared to industrial trials and the optimization of an existing process is demonstrated. Ausscheidungshärtende ferritisch perlitische Stähle werden in der Automobilindustrie für geschmiedete Motor- und Fahrwerkskomponenten eingesetzt. Unter Einsparung teurer und zeitaufwendiger Wärmebehandlungen werden die geforderten Eigenschaften durch kontrolliertes Abkühlen aus der Schmiedehitze eingestellt. Darum muß die gewünschte Austenitstruktur durch die Umformvorgänge bereits vor der Phasenumwandlung eingestellt sein. Die Planung mehrstufiger Schmiedevorgänge, die darauf zielt, Gefügeinhomogenitäten durch konventionelle “trial and error” Verfahren zu vermeiden, ist nicht nur zeit- und kostenaufwendig sondern führt darüber hinaus nicht immer zu optimalen Ergebnissen. Daher ist es anzustreben, Informationen über die Gefügeentwicklung eines vorgegebenen Umformprozesses durch Computersimulationen zu erlangen und eine Prozeßoptimierung durch Variationsrechnungen vorzunehmen. Ein solches Modell wird auf die Produktion eines Pleuels aus 49MnVS3 angewendet. Die Simulationsergebnisse werden mit Messungen aus einem industriellen Fertigungsprozeß verglichen. Eine Optimierung dieses Prozesses wird gezeigt.

Influence of microalloying additions on thickness of grain boundary carbides in ferrite–pearlite steels

AbstractFor a series of plain C and microalloyed steels at two levels of Mn, the growth of grain boundary carbides has been monitored after heating to 920°C and cooling at 40 and 150 K min−1 through the austenite–ferrite/pearlite transformation down to room temperature. In pearlite free steels, on cooling to room temperature, all the C in solution in the ferrite is able to precipitate as carbides at the boundaries and the grain boundary carbide thickness is dependent on the number of nucleation sites for precipitation. Increasing the cooling rate increases the number of sites and reduces the carbide thickness. In ferrite–pearlite steels, the grain boundary carbides form the ‘tails’ to the pearlite colonies. The thickness of the grain boundary carbide is related to the pearlite reaction, since the temperature at which this occurs controls both the thickness of the carbide nuclei and the amount of C available for precipitating out on these tails. Increasing the cooling rate and Mn content causes a decrease ...

Influence of microalloying additions on thickness of grain boundary carbides in ferrite–pearlite steels

Influence of microalloying additions on thickness of grain boundary carbides in ferrite–pearlite steels

Effect of Microstructures on the Fatigue Strength of Notched Specimen in Ferritic-Pearlitic Steels.

Rotating bending fatigue tests were carried out on the circumferential notched specimen of three kinds of carbon steel with nearly equal ferrite grain sizes of 20μm but different volume fractions of pearlite. Fatigue tests were also carried out for 0.15% carbon steel with ferrite grain size of 50μm and 0.45% carbon steel with ferrite grain size of 5μm. The effect of microstructures on the fatigue strengths σws (the limit stress for slip band), σw1 (the limit stress for macrocrack initiation), and σw2 (the limit stress for fracture) is discussed by comparing these values between three kinds of carbon steel. The main results are as follows : (1) Since σws is localized to a highly specified region, variation of Ktσws is small irrespective of notch root radius. (2) If the grain size of ferrite is nearly equal, variation of σw1 is small irrespective of pearlite volume fraction under the certain amount of pearlite. (3) In medium carbon steel, σw2 increases with increasing grain size of ferrite. (4) Notch root radius at the branch point ρo varies with the grain size of ferrite.

フェライトーパーライト熱延鋼板の疲労特性に及ぼす強化機構の影響

フェライトーパーライト熱延鋼板の疲労特性に及ぼす強化機構の影響